Ahead of the bell: Apple

Apple shares continued to slide for a second day before the opening bell, a day after the company posted its worst one-day stock drop in four years.

On Wednesday, the Cupertino, Calif.-based company's shares closed down 6 percent at $538.79, erasing $35 million in market capitalization. Speculation abounded as to the cause.

CNBC reported that part of the drop stemmed from a clearinghouse's decision to boost margin requirements on the stock, while Bloomberg Businessweek attributed it to worries that the company could lose smartphone and tablet market share in China.

Some believe that Apple's absence from the growing list of companies declaring a special dividend ahead of year's end is partly to blame.

Meanwhile, Apple's shares are on track to reach a "death cross" in the next few days, a technical term alluding to the point at which long-term and short-term trends for the stock cross paths, with long-term moving average breaking higher.

A death cross can indicate a bear market ahead for a company and usually accompanies a high volume of trading, which has been seen in recent days with Apple stock.